The present invention relates to improvements in devices for making holes, and more particularly to improvements in rotary material removing tools of the type wherein a rod-like or an analogous support carries several holders for knives in the form of blades or the like. Still more particularly, the invention relates to improvements in rotary boring, drilling, reaming, milling or analogous tools of the type wherein the front end portion of the rotary support carries two knife holders disposed in a plane which is normal to the axis of the support and wherein the holders are shiftable relative to the support in response to loosening of clamping means which normally prevents any displacements of the holders relative to each other and/or relative to the support.
It is already known to install two knife holders at the front end of an elongated rod-like support which receives torque from the prime mover of a milling, boring or like machine. The holders are adjustable relative to each other and with reference to the support so as to move their knives nearer to or further away from each other, depending on the desired diameter of the hole or bore which is to be machined, enlarged or finished by the tool. The holders have slots for clamping screws which normally secure the holders to the support but allow for adjustment of the holders when the screws are loosened. In accordance with a presently known proposal, the clamping means comprises two screws each of which extends through an elongated slot of the corresponding holder and meshes with the support. The screws are parallel to the axis of rotation of the support and extend through bores in a clamping plate which overlies portions of the holders. The holders are adjacent to one another and are held against movement relative to the support as long as the clamping screws are applied with sufficient force. The aforementioned slots of the holders are only partially overlapped by the clamping plate so that chips, shavings and/or other foreign bodies are likely to penetrate into the slots to thus prevent any adjustments or to interfere with accurate adjustment of holders with reference to the support. Moreover, foreign matter which enters and fills the elongated slots of the holders interferes with removal of shavings or chips from the locations where the cutting edges of the knives remove material from a workpiece or the like.